Al-2N掺杂量对ZnO光电性能的影响

与本文相近的Al-2N掺杂量的范围内, 对ZnO掺杂体系吸收光谱分布红移和蓝移两种实验结果均有文献报道, 但是, 迄今为止对吸收光谱分布尚未有合理的理论解释. 为了解决该问题, 本文采用基于密度泛函理论的广义梯度近似 平面波超软赝势方法, 用第一性原理构建了两种不同掺杂量的Zn_0.98148Al_0.01852O_0.96296N_0.03704和Zn_0.96875Al_0.03125O_0.9375N_0.0625超胞模型. 在几何结构优化的基础上, 对模型能带结构分布、态密度分布和吸收光谱分布进行了计算. 计算结果表明, 在本文限定的掺杂量范围内, Al-2N掺杂量越增加, 掺杂体系的体积越减小, 体系总能量越升高, 体系稳定性越下降, 形成能越升高, 掺杂越难; 所有掺杂体系均转化为简并p型化半导体, 掺杂体系最小光学带隙均变窄,吸收光谱均发生红移; 同时发现掺杂量越增加, 掺杂体系最小光学带隙变窄越减弱, 吸收光谱红移越减弱. 研究表明: 要想实现Al-2N共掺在ZnO中最小光学带隙变窄、掺杂体系发生红移现象, 除了限制掺杂量外, 尺度长短也应限制; 其次, Al-2N掺杂量越增加,掺杂体系空穴的有效质量、浓度、 迁移率、电导率越减小,掺杂体系导电性能越减弱. 计算结果与实验结果的变化趋势相符合. 研究表明, Al-2N共掺在ZnO中获得的新型半导体材料可以用作低温端的温差发电功能材料.

Effects of Al-2N doping on the photoelectric properties of ZnO

In a similar range of Al-2N doping amount to that in the present paper, the absorption spectra of ZnO doped system and two kinds of experimental results have been reported in the literature. However, there is no reasonable explanation for the absorption spectra of ZnO doped system. In order to solve the problem, all calculations in the present paper are carried out by the CASTEP tool in the Materials Studio software based on the first principal ultrasoft pseudopotential of the density functional theory, and the geometric structures of ZnO, Zn_0.98148Al_0.01852O_0.96296N_0.03704 and Zn_0.96875Al_0.03125O_0.9375N_0.0625 systems are constructed by first-principal. All the models are based on the optimization of the geometry structure. And the distribution of the band structure, the density of states and the absorption spectra of the doping system are calculated by the method of GGA+U. The results indicate that in the range of the doping content restricted in the present paper, the bigger the doping amount of Al-2N, the smaller the volume of doped system is; the higher the total energy, the more the stability decreases; the higher the formation energy, the harder the doping becomes and the narrower the optical band gap of doped system. Meanwhile, the higher the Al-2N doping content, the narrower the optical bandgap of the doping system becomes, which suggests that the more significant the red shift of absorption spectrum of Al-2N doped ZnO system is. Therefore, the doped system is controlled within the doping content in experiment to obtain the narrow optical band gap and red shift in absorption spectrum in Al-2N doped ZnO, in addition to the control of lower nanoscale of Al-2N doped in ZnO. At the same time, all doping systems are p-type degenerated semiconductors. Then, the higher the Al-2N doping content, the smaller the relative concentration of free holes of doped system is; the smaller the hole effective mass, the lower the mobility is; the lower the hole conductivity, the worse the conductive property of doping system is. The calculated results are in agreement with the experimental results. The research shows that Al-2N co-doped ZnO can be a new type of semiconductor material, a functional material which is used at low temperature end of thermoelectric power generation.